Vapor-electric device



Jan. 17, 1950 N. c. FULMER VAPOR-ELECTRIC DEVICE Filed Oct. 13, 1948Fig.6.

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Trigger Circuit Source [0000 20000 30000 40000 50000 Resis tunce of RFig.3.

INVENTOR Norman- C. Fulmer.

J JW ATTORNEY Patented Jan. 17, 1950 2,495,165 VAPOR-ELECTRIC DEVICENorman C. Fulmer, Montclair, N. J

Electric Corporation, burgh, Pa., a corpora Westinghouse assignor toEast Pittstion of Pennsylvania Application October 13, 1948, Serial No.54,345

3 Claims.

My invention relates to a vapor-electric device and particularly to animpulsing system for applying periodic control impulses to the makealiveelectrode of an ignitron.

In the operation of vapor-electric devices provided with make-aliveelectrodes or so-called ignitors it has long been customary to charge acapacitor from a suitable source and to discharge the capacitor toprovide an ignition or make-alive impulse to start the operation of thevapor-electric device.

In the use of such control systems there have been occasions wheredifficulty has been experienced in maintaining the impulses in the exactsequence or time relation desired. Heretofore, it has been customary toutilize an electric valve, particularly an electric valve of the'gridcontrolled discharge type for controlling the impulse.

It has heretofore been customary to provide a suitable biasing orblocking potential to the grid of the control valve to prevent prematureor unscheduled discharges and to provide a triggering impulse toovercome the bias at the instant it is desired to initiate conduction.

If the biasing potential is sufficient to bias the electronic tube so asto insure adequate rapidity of cutoff or deionziation immediatelyfollowing the condenser discharge, it is necessary to use a high biaspotential and consequently a, high triggering potential. Since highpotential requires extra insulating precautions and protection, andsince a higher triggering potential requires a more complex triggeringcircuit, this produces an expensive and unyielding control system.

I have found that this high potential control system may be modified byproviding a biasing potential proportioned to the rate of charge of thecapacitor. In other words, a very high biasing potential at theinitiation of the charging period which is reduced at the end of thecharging period to a relatively nominal biasing potential which may bereadily overcome by a reasonable triggering potential. I have found thatthis biasing potential may be most easily obtained from an impedanceconnected in series with the charging current of the capacitor andapplied to the grid of the electric valve in parallel with thetriggering potential.

It is accordingly an object of my invention to provide an impulsingcircuit having a self-biasing component for the electric valve thereof.

A further object is to obtain grid bias voltage without the use of aseparate battery or power supply.

A still further object is to obtain grid bias voltage as an inherentpart of the circuit.

It is a further object of my invention to provide an impulsing circuitin which the bias is proportional to the rate of charge of a capacitor.

Other objects and advantages of my invention will be apparent from thefollowing detailed description, taken in conjunction with theaccompanying drawing, in which:

Figure 1 is'a diagrammatic impulsing circuit;

Fig. 2 is a similar illustration of an impulsing circuit embodying myinvention;

Fig. 3 is a graphical illustration of the biasing potential applied tothe grid of the control valve, and

Fig. 4 is a graphical illustration of the characteristics of animpulsing system according to my invention.

In an exemplary embodiment of my invention a load device I is suppliedwith unidirectional po-' tential from an alternating-current circuit 2by means of a vapor-electric device 3 of the makealive typ commonlycalled an ignitron. The vapor-electric device 3 comprises an evacuatedcontainer 4 having therein a liquid cathode 5 usually comprised ofmercury, allium, sodium, potassium, caesium or other suitable materialor materials.

Cooperating with the cathode 5 is an anode 6, usually composed ofgraphite or metal, in spaced insulated relation to the cathode 5.Conduction in the vapor-electric device 3 is secured by means of amake-alive electrode I, sometimes illustration of an F called anignitor, in contact with the surface of the cathode pool 5.

My impulsing system for supplyingthe necessary control impulses to themake-alive electrode 1 comprises a source In of high voltageunidirectional potential. This may be derived from any suitable devicenot herein shown. In order to stabilize the high voltage potential, Iprefer to connect a capacitor ll of high value across the terminals l2and I3 of the source ill. A firing capacitor 15 connected by chargingcircuit In to the terminals l2 and [3 of the high voltage source Inprovides the actual source of potential for the impulse.

The firing capacitor 15 is charged from the high voltage source It bymeans of a current control impedance l6 preferably in the form of aresistor Re. The impedance I6 is of a value to determine the rate ofcharge and consequently the time during which the capacitor l5 will becharged from the source H3. After the firing capacitor l5 has beensufficiently charged, a triggering circuit 20 will supply a controlimpulse to the grid 2| of a control valve 22 in the discharge circuit 23for the capacitor l5, which discharge circuit 23 connects the make-aliveelectrode 1 across the potential of the capacitor l5. Preferably animpedance 24, usually in the form of a resistor R, is supplied in thedischarge circuit 23 to control the time interval during which makealivepotential is applied to the make-alive electrode and to limit the peakdischarge current through the control valve 22 to a safe value.

Heretofore, it has been customary to provide a constant biasingpotential 25 to the grid 2| of the control valve 22. In order to beeffective this biasing potential 25 must be of suflicient value toprevent accidental operating of the control valve 22 at any intervalduring the charging period of the capacitor |'5. Consequently, thetriggering potential 20 must be sufiicient to adequately overcome thisconstant biasing potential 25.

In order to eliminate the necessity for a source of constant biasingpotential 25 and the inconvenience connected therewith, I have obtainedfrom the charging circuit H! a biasing potential proportional to therate of charge of the firing capacitor 5. In order to obtain thispotential, I have provided an impedance 26, usually in the form of aresistor RB, connected in the negative side of the charging circuit l4and supplying a circuit 21 for applying the potential drop across thisimpedance 26 to the grid 2| of the control valve 22. Preferably, asuitable capacitor 28 is provided across the impedance 26 providing thebiasing potential. The potential derived from the impedance 26 is of arelatively high value at the instant of initiation of the charge andthen gradually reduces as the charge on the capacitor 5 builds up andthe charging current decreases. This is shown in graphical form in Fig.3. In the instant of the beginning of the charge a very high potential30 appears across the impedance 26 and as the charge builds up thispotential decreases according to the curves 3| of Fig. 3. Then at theinstant the capacitor 5 is discharged and starts to recharge, a highpotential 30 is immediately applied to the grid 2| to prevent anyundesired misfire or undesirable operation of the electric valve 22.

The necessary characteristics for relation of the component parts of mycircuit are best illustrated in graphical form in Fi 4. The range overwhich the device is operative is determined by the relative values ofthe resistance 24 of the discharge circuit 23 and the biasing potentialsource 26 in relation to the applied voltages. Assuming that theresistance R in the discharge circuit 23 has a value of ohms and thehigh voltage source ID a value of 3000 volts or 3 kilovolts, theresistance RB of the impedance 26 has been determined to be not lessthan 1500 ohms or not more than 25,000 ohms. These points were selectedby decreasing the impedance of RB to a point a where the circuitmisbehaved, usually by improperly firing and then increasing theimpedance of RB until the circuit again misbehaved at point b, usuallyby failure to fire. During this intermediate period from a to b thecircuit operated satisfactorily. Then with the impedance R changed to 80ohms the circuit was again operated on the low side until it misbehaved,which was found to be at point 0 at a value of 6000 ohms. Similarly, theimpedance was increased until at point d it again misbehaved at a valueof approximately 19,000 ohms.

Other points on the curves of Fig. 4 were similarly obtained by changingthe value of the high voltage source In and the impedance of 24. Thesolid line curves of Fig. 4 were the maximum and minimum impedance of RBof various potentials with a discharge impedance 24 of 10 ohms and thedotted line curves are the same characteristic with a dischargeimpedance 24 of ohms. Values of other components in this experimentalcircuit were as follows: Resistor Rc, 50,000 ohms; condenser 5, 0.02microfarad; electric valve 22, WL677; trigger voltage 20, 140 voltspeak. The frequency of operation was cycles per second.

In the operation of the system according to my invention, the highpotential source 0 is applied to the firing capacitor l5 whichautomatically applies the bias potential to prevent discharge of thecontrol valve 22 in series with the make-alive electrode 1. Also appliedto the control grid 2| of the control valve 22 is a periodic triggeringpotential 20, which is in phase with and may be obtained from thepotential 2 applied to the anode 6 of the make-alive device 3. As willbe apparent, the biasing potential 30 of the impedance 26 at thebeginning of charging of the capacitor I5 is sufiiciently high toprevent any possibility of undesirable operation. Then as the chargingperiod is completed, the biasing potential is reduced so that thetriggering potential 20 or control impulse for the control tube 22readily overcomes the biasing potential and permits absolute control ofthe discharge to the make-alive electrode 1 and consequent accuratecontrol of the current through the make-alive device 3.

While for the purposes of illustration I have shown a specificembodiment of my invention, and described my invention to the best of mypresent understanding, I wish it to be understood that I am not limitedto the example or explanation herein given, and it is apparent that manymodifications can be made therein without departing from the true spiritof my invention or the scope of the appended claims.

I claim as my invention:

1. A control system for a vapor-electric device comprising a cathodespot initiating electrode in said device, a source of substantiallydirect our- 4 source, impedance means connected between said source andsaid capacitor for controlling the rate of charge of the capacitor,circuit means including a grid controlled electric valve and a currentlimiting impedance for connecting said electrode across the terminals ofsaid capacitor, circuit means energized by current flow to saidcapacitor for impressing a negative bias potential on the grid of saidgrid controlled valve and means for periodically impressing a positivetrigger potential on the grid of said valve.

2. A control system for a vapor-electric device comprising a make-alivetype electrode in the device, a source of unidirectional controlpotential, a capacitor connected across said control potential,impedance means connected in series circuit relation between said sourceand said capacitor at least a portion of said impedance being connectedbetween the negative terminal of said source and said capacitor, adischarge circuit for said capacitor including in series circuitrelation said make-alive type electrode, a grid controlled electricvalve and a current limiting impedance means, circuit means forimpressing the negative potential drop through that portion of theimpedance means connected to the negative terminal of the source on thegrid of said grid controlled electric valve, a source of periodictrigger potential and connections impressing the trigger potential onthe grid of said valve.

3. A control system for supplying periodic control impulses to anexciting electrode comprising a source of direct current controlpotential, a oapacitor connected to be charged from said source, animpedance between said source and said capaoitor, a discharge circuitconnecting said exciting electrode across said capacitor, a gridcontrolled valve in said discharge circuit, circuit means for impressinga portion of the potential drop across said impedance 0n the grid ofsaid grid controlled valve, a source of periodic trigger potential andconnections for impressing the periodic trigger potential on the grid ofsaid valve.

NORMAN C. FULMER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,889,608 Lord Nov. 29, 19322,008,730 Smede July 23, 1935 2,097,066 Hoover Oct. 26, 1937 2,100,700Schlesinger Nov. 30, 1937

